With the development of the IP network toward the direction of carrying multiple services, the services such as the Next Generation Network (“NGN” for short), the Internet Protocol Television (“IPTV” for short) put forward higher and higher demands on the reliability and real-time of the network, and the traditional ring network protection Spanning Tree Protocol (“STP” for short) technology of the second-layer network of the access network gradually cannot satisfy the requirements of fast convergence and link switching.
RFC3619 has defined an Ethernet automatic protection switching method. The method solves the problem of slow convergence of network failure of the Ethernet device in a ring-type network topology, and the convergence time can be limited to be within 50 ms by using the method. A RFC3619 ring is formed by connecting a plurality of nodes, wherein one node is defined as a master node, the master node is also called as a ring protecting link affiliation node in some technologies, and other nodes are defined as transit nodes. The two ports of the master node on the ring are defined as a primary port and a slave port respectively, and the link directly connected to the slave port may be called as ring protecting link. The ring protecting link is a link on the ring where the service communication data is blocked when there is not any failure or request in the Ethernet ring so as to prevent a closed ring. When any of the links on the ring is not failed, the master node blocks the service data forwarding function of the slave port, i.e., the master node blocks the ring protecting link, such that the service data cannot pass through the slave port of the master node, which ensures that the service VLAN (Virtual Local Area Network) cannot form a closed loop and prevents the “broadcast storm” caused by the closed loop. When a link on the ring is failed, the master node unblocks the service data forwarding function of the slave port, i.e., the master node unblocks the ring protecting link, such that the service data can pass through the slave port of the master node, which ensures the connectivity of the service data, and the interruption will not occur.
FIG. 1a is a topological diagram of a RFC3619 ring, formed by nodes S1, S2, S3 and S4, wherein the master node (MASTER) is S2, and other nodes S1, S3 and S4 are transit nodes (TRANSIT). The two ports of the master node S2 on the ring are respectively the primary port and the slave port, wherein port 2 is the primary port (P) and port 1 is the slave port (S). As shown in FIG. 1b, when the states of the links on the ring are in good condition, the master node S2 blocks the service data forwarding function of the slave port 1 to prevent a closed loop from presenting in the network to form the “network storm”; and as shown in FIG. 1c, when a link on the ring is failed, the master node S2 unblocks the service data forwarding function of the slave port 1 to make the service data re-connected.
Though the RFC3619 solves the problem of fast convergence of a single physical ring network very well, the actual networking is usually quite complicated and a situation exits that a plurality of physical rings are tangent with each other. As shown in FIG. 2a, a topological structure is shown that a plurality of RFC3619 rings are intersected, S1, S2, S3, S4 in the figure form ring 1, in which S2 is the master node, and port 2 of node S2 is the primary port, port 1 is the slave port; S3, S4, S5, S6 form ring 2, in which S6 is the master node, and port 2 of node S6 is the primary port, and port 1 is the slave port. When any of the links on the rings is not failed, the master nodes S2 and S6 respectively block their respective slave ports. When the shared path of the two rings, i.e., the link between nodes S3 and S4, is failed, as shown in FIG. 2b, a link on ring 1 is failed, the master node S2 unblocks the slave port, and the link in ring 2 is failed, the master node S6 unblocks the slave port, then a closed loop of “super loop” appears on the whole ring, the “network storm” is formed and the network is failed.
The same problem will occur when the other Ethernet ring protection technologies similar to the RFC3619 for protecting the single ring is applied to multiple rings, i.e., the failure of the shared path may make a plurality of ring protecting links unblocked, which finally causes the “super loop” to appear on the whole ring and forms the network failure of “network storm”.
In the present text, a port being blocked means that the port is configured not to forward the service data when it is blocked, and a port being unblocked means that the port is configured to forward the service data when it is unblocked, wherein the forwarding of the protocol frame of Ethernet ring protection will not be affected no matter the port is blocked or unblocked. A link being blocked means that one of two adjacent ports of the link is blocked or both ports are blocked, and the service data cannot be forwarded by one of the two adjacent ports of the link and thus cannot pass through the blocked link; and a link being unblocked means that both the two adjacent ports of the link are unblocked, and the service data may be forwarded by the two adjacent ports of the link.